total_populations need to change with mortality

[petrasovaa]

As far as I understand, total_populations should be changing when hosts die, probably with movements too? Right now, total_populations is not being changed but it is not const in run_step.

[ChrisJones687]

We have been using total_populations in all of our models thus far as the max value across the landscape. Typically, this is 100, and our host layer is treated as a percentage of the total area based on how our host maps are made. We could probably make this a single value that doesn't change across the landscape to save on memory.